Stable production of proteins, including biologics, can be accomplished by transfecting host cells with vectors containing DNA that encodes the protein. Maintenance of the vector in the cell line can be achieved through a variety of means, including extrachromosomal replication through episomal origins of replication. Episomal vectors contain an origin of replication that promotes replication of the vector when the sequence is bound by a replication initiation factor. Episomal vectors have several advantages over vectors that require insertion into the host genome. For example, episomal vectors decrease phenotypic changes in the cell that may result from integration of a vector into the host genome. Episomal vectors may also be isolated from the transfected cells using standard DNA extraction protocols.
With the evolving importance of therapeutic proteins, i.e., biologics, efforts must be made to optimize protein production, while improving efficiency of the overall production process. Thus, improvements in efficiency must be weighed against the protein production capacity of the vector. There is a need for better expression systems that provide efficient cloning options, as well as high levels of the desired protein product. It would be advantageous to decrease the number of cloning steps involved in the production of biologics, especially antibodies, to improve time requirements and minimize cost. It would also be advantageous to provide vectors that provide adequate protein production for both small and large scale cell cultures. The present invention overcomes the limitations of conventional vectors, by providing additional advantages that will be apparent from the detailed description below.